I've been meaning to post this for a few weeks now, but this is the pukka, gen dit, from the man himself,

Charlies Hole-in-the-Wall JC recipie.

This is verbatum

The Mix
Get an empty 1.5 litre pop bottle
Just under .5 litre lime cordial, the rest lemon squash
add Angustora Bitters to turn into rusty colour, varied according to taste.

The JC
Add 1 tot mix to 1 tot gin and top up with soda water and ice.

He goes on to say:

"However the exclusive surroudings, the Jinesse [sic] of the clientelle and the soft music of the piano tinkling in the background, not to mention the youthful beauty, elegance and charm of the bar person, undoubtedly enhances the taste of a JC.